If you want to publish your book on Google Play or Google Book Store then first of all you being a Google Play Partner. May be waiting for 7 or 10 days to getiing approval your partnership. If already have a Google Play Partner account then you following this steps.
Step 1: Go to Google Book Publisher website : play.google.com/books/publish and login your approved partnership account.
Step 2: Click book catalog and then click +Add book
Read also: How to create a Google Play Partner
Step 3: Click metatag and fill books details.
Read also: How to get ISBN in free
Step 4: Upload your book catalog or content
Step 5: Set book prices.
Step 6: Go book settings and set publisher logo or website.
Congratulation! All done your book is available on Google Play.